1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of handling proximity information transmission in a wireless communication system and a related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
In the LTE system, a UE supporting a closed subscriber group (CSG) feature can transmit proximity information to the network for triggering inbound mobility (namely handover) to a CSG/hybrid cell when the UE is configured proximity indication reporting by the network. The UE supporting the CSG feature has a CSG whitelist which contains one or more CSG identities associated with CSG cells on which the UE is allowed access. The CSG cell is associated with a small coverage base station which may be deployed for magnificent advantages, such as the high bandwidth wireless internet access in the home and office, and efficient and cost-effective capacity solution for indoor coverage, whereas the hybrid cell is accessed as a CSG cell by a UE whose CSG whitelist contains a CSG identity of the cell and as a normal cell by all other UEs.
As to an operation of the inbound mobility, the proximity information is sent to the network (i.e. the E-UTRAN, an eNB, or a base station) when the UE enters proximity of a cell whose CSG identity is in the CSG whitelist of the UE. The network configures the UE with a measurement configuration including a measurement gap if needed after the proximity information is received. The UE performs the measurement to the CSG cell, so as to generate a measurement report to the network for a handover preparation. Moreover, the network configures the UE with system information (SI) reporting. The UE reads system information of the CSG cell, and then sends an SI report including the CSG identity of the CSG cell to the network, so that the network can check whether the CSG cell is allowed for access based on the CSG identity and the CSG whitelist for the UE. In other words, the network determines whether to handover the UE to the CSG cell according to the measurement report and the SI report, and sends a handover command to the UE when the network decides to handover the UE to the CSG cell.
In addition, after sending the “entering” proximity information to the network, if the UE determines that it is no longer near the entered CSG cell, the UE shall send the “leaving” proximity information to the network. Otherwise, the network does not know that the UE is left, and may ask the UE to perform the measurement to the left CSG cell, thereby causing radio resource waste.
However, due to unclear specification for proximity information transmission in the LTE system, the UE may not perform the inbound mobility to the CSG/hybrid cell. In addition, several scenarios are described as follows.
In the first scenario, proximity information sent by the UE may not be received by the network due to a handover or an RRC connection re-establishment procedure (e.g. caused by radio link failure, RLC unrecoverable error, MAC random access error, etc). If the proximity information is not received by the network, the inbound mobility to CSG/hybrid cells cannot be started since the network does not know that the UE enters proximity of CSG cells in the CSG whitelist of the UE. Thus, a user of the UE may complain why the UE cannot use the CSG cell for communication. The detailed description associated with the operation of the inbound mobility can be referred from above, so it is omitted herein.
In the second scenario, the UE connects to a first eNB and enters the proximity of cells whose CSG identities are in the CSG whitelist of the UE. Therefore, the UE sends proximity indication to the first eNB for the inbound mobility. Meanwhile, the first eNB sends a handover command to command the UE to handover to a second eNB. In addition, the handover command enables the proximity indication reporting, so that the UE is allowed to transmit the proximity information to the second eNB. However, the UE is still in the proximity of the cells after the UE is handover to the second eNB. In other words, the UE does not leave the proximity of the cells after handover to the second eNB. In this situation, the UE does not send the proximity information since the UE never leaves the proximity of the cells. Therefore, the second eNB does not know the UE is in the proximity of the cells, and thereby cannot handover the UE to a CSG cell or cannot configure the UE system information (SI) reporting.
In addition, the UE connecting to the first eNB is configured SI reporting. The UE sends the SI report including CSG identity to the network, so that the network can determine whether the CSG cell is allowed for access according to the CSG identity. However, after the UE is handover to the second eNB, the UE does not send the SI report since the SI reporting configuration from the first eNB is removed. Therefore, the second eNB does not receive the SI report from the UE, and thereby cannot handover the UE to a CSG cell.
Furthermore, the abovementioned situation may occur in a universal mobile telecommunications system (UMTS). For example, the UE provides a serving radio network controller (SRNC) with the proximity information when it is near or left a CSG/hybrid cell whose CSG identity is in the UE's CSG whitelist. Due to similar behavior in the UMTS system, the foregoing problems arise as well.